and (maintenance) float charge stages. All lead–acid batteries, irrespective of type, are quick to bulk charge to about 70% of capacity during which the battery will accept a large current input, determined at a voltage setpoint, within a few hours (with a charge source capable of supplying the design C-rate bulk stage current for a given Ah battery). However, they then require a longer time spent in the current-tapering off intermediate absorption charge stage after the initial bulk charge, when the LA battery charge acceptance rate gradually reduces, and the battery will not accept a higher C-rate. When the absorption stage voltage setpoint is reached (and charge current has tapered off), the charger switches to a float voltage setpoint at a very low C-rate to maintain the battery's fully charged state indefinitely (the float stage offsets the battery's normal self-discharge over time). If the charger fails to supply a sufficient absorption stage charge duration and C-rate (it 'plateaus' or times out, a common fault of cheap solar chargers), and a suitable float charge profile, the battery's capacity and longevity will be dramatically reduced. To ensure maximum life, a lead–acid battery should be fully recharged as soon after a discharge cycle as possible to prevent sulfation, and kept at a full charge level by a float source when stored or idle (or stored dry new from the factory, an uncommon practice today). When working a discharge cycle, a LA battery should be kept at a DOD of less than 50%, ideally no more than 20-40% DOD; a true LA deep-cycle battery can be taken to a lower DOD (even an occasional 80%), but these greater DOD cycles always impose a longevity price. Lead–acid battery lifetime cycles will vary with the care given, with best care they may achieve 500 to 1000 cycles. With less careful use, a lifetime as few as 100 cycles might be expected (all dependent upon the use environment too). Because of calcium added to its plates to reduce water loss, a sealed AGM or gel battery recharges more quickly than a flooded lead–acid battery of either VRLA or conventional design. Compared to flooded batteries, VRLA batteries are more vulnerable to thermal runaway during abusive charging. The electrolyte cannot be tested by hydrometer to diagnose improper charging that can reduce battery life. AGM automobile batteries are typically about twice the price of flooded-cell batteries in a given BCI